1. Field of the Invention
This invention relates to a method of making blow-molded perforated tubing and perforated tubing made by said method. 2. Prior Art Statement
Perforated tubing may be used for irrigation or for drainage. Conventionally, perforated tubing is made by first forming the tubing and then perforating the tubing by punching or by cutting holes in the tubing using a rotating hook knife or saw. In prior art methods, the materials used in the tubing had to be stiff to obtain good results since softer materials would tend to deflect away from the punch and the cutters.
Perforated tubing is often made in a corrugated configuration since the corrugations provide structural support for maintaining the shape of the tubing. Corrugated perforated tubing, and methods of making the same, are described in the following U.S. Patents:
______________________________________ Inventor U.S. Pat. No. Date ______________________________________ Hegler, et al 4,184,831 January 22, 1980 Fales 4,163,619 August 7, 1979 Maroschak 3,861,153 January 21, 1975 Maroschak 3,861,152 January 21, 1975 Maroschak 3,802,202 April 9, 1974 Maroschak 3,789,615 February 5, 1974 Maroschak 3,747,352 July 24, 1973 ______________________________________
Conventionally, blow-molded corrugated tubing is made by a method and apparatus described in U.S. Pat. No. 3,391,424 to Drossbach, which was issued July 9, 1968. As described in the Drossbach patent, perforated tubing is made by blow molding the tubing using the apparatus apparatus illustrated in FIG. 1. and perforating the tubing using a rotating cutter as is illustrated in FIG. 5 therein.